Now, the similarities may run even deeper. Contrasting previous statements, ESPN New York's Wallace Matthews reported on Sunday that Teixeira's injury is not actually an ECU tendon strain but rather a partially torn tendon sheath—the exact same diagnosis Bautista received last year (h/t Stephania Bell, ESPN).

Yet while Bautista's injury ultimately required season-ending surgery to reconstruct the sheath, Matthews' report states the Yankees do not yet expect Teixeira's new diagnosis to necessitate surgery or prolong his projected recovery of eight to 10 weeks. Why is that the case? Simply, Bautista's sheath tear yielded an "unstable" ECU tendon. Teixeira's did not.

Jonathan Daniel/Getty Images

Jose Bautista also suffered a partially torn ECU tendon sheath last season. He developed ECU tendon instability and ultimately required season-ending surgery to repair the tendon and sheath.

Despite Teixeira's less-complicated injury, if he were to develop ECU tendon instability during his recovery, he could follow a course similar to Bautista's. To understand why that is, it helps to break down the ECU and its function.

The ECU is actually a forearm muscle. Like all muscles, the ECU is connected to a bone by a thin, tough tendon. Specifically, the ECU tendon attaches its muscle body in the forearm to the bone that forms the base of the pinky finger.

Like all muscles, when the ECU muscle body contracts it pulls on its tendon, which in turn pulls on the bone to which it is attached. The end result is—with the palm facing up—bending of the wrist inward and downward.

From a baseball perspective, the ECU is important for generating power in a baseball swing. Both left-handed and right-handed hitters need strong ECUs in both wrists to help snap the bat through the strike zone during the middle portion of the swinging motion.

The above diagram shows the muscles of the back of the hand and forearm. The white ECU tendon can be seen connecting the purple ECU muscle body to the base of the pinky finger. Photo from Wikimedia Commons.

Since it is used extensively in baseball—especially with power hitters like Teixeira and Bautista—the ECU is prone to injury. Tendon injuries, known as "strains," occur when a muscle overloads its tendon, causing it to over-stretch or tear.

Overuse of a worn-down tendon can also produce a strain, as can an outside force briskly stretching a simultaneously contracting tendon—such as a baseball forcing the bat slightly backward at contact. Bautista pointed out to Bell his suspicion that such an injury mechanism may be unknowingly widespread throughout baseball.

On the other hand, even when fully healthy, a tendon is pulled very sharply across other tissues within the wrist when its muscle contracts. As Bell describes in her blog, that is where the protective tendon sheath comes in.

Imagine placing a hollow half cylinder over an electrical cord. The cord represents the muscle tendon, and the half cylinder represents the sheath. While under the cylinder, the cord can move forward and backward, but it cannot move to either side. It also cannot come into contact with anything around it.

In short, the sheath encases and protects the tendon.

In this video, an unstable ECU tendon can be seen moving over bone.

Still, similar to how too much force can tear a tendon, too much tendon motion can likewise tear a sheath. What's more, sheaths are relatively quite flimsy when compared to tendons.

A torn sheath doesn't necessarily affect the ECU muscle per se. The muscle can still contract and pull on the pinky finger on its own.

However, as mentioned, a tendon without a fully intact sheath sometimes gains the ability to move from side to side—called an "unstable" tendon. Unstable tendons can cross over and around bone and other tissues. Over time, the repeated tracking of a tendon over tissues such as bone causes damage, damage that can range from mild tendinitis to overt tendon rupture.

Fortunately, Yankees team physician Dr. Chris Ahmad determined Teixeira's ECU tendon to be stable despite the sheath tear. In other words, unlike Bautista, Teixeira's partial sheath tear is not extensive enough to allow the tendon to move around freely within the wrist.

Can the Yankees compete for the AL East crown if Mark Teixeira misses more than 8-10 weeks?

Yes; the roster is deep enoughYes, but they would need to trade for a new first basemanNo; their injury troubles are already far too extensiveNo; they are an inferior team even when healthyOther (leave comments below)Submit Votevote to see results

Can the Yankees compete for the AL East crown if Mark Teixeira misses more than 8-10 weeks?

Yes; the roster is deep enough

14.9%

Yes, but they would need to trade for a new first baseman

23.3%

No; their injury troubles are already far too extensive

39.0%

No; they are an inferior team even when healthy

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Other (leave comments below)

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Nevertheless, injured tissues are weaker tissues, and weaker tissues are prone to further, more serious injury. For that reason, Teixeira must rest his arm in order to allow the sheath to heal. Placing stress on it too early could cause it to progress to a full tear and make surgical repair and reinforcement necessary.

Additionally, if Teixeira were to work out too soon and turn his stable ECU tendon into an unstable one, he would risk the previously mentioned injuries in addition to requiring surgery. In the worst-case scenario, a frank ECU rupture could seriously jeopardize his career as a power hitter.

As such, Teixeira and the Yankees need to be patient. They also need to be willing to accept a timeframe of longer than eight to 10 weeks should Teixeira's healing progress more slowly than expected.

Unfortunately, extended missed time will likely lead to lost muscle strength. Even after he returns to action, it will take time for his strength, and therefore his power, to return to its pre-injury level, and he likely won't have the same pop in his bat until it does.

This is one of those things I can't come back too early. . .I don't know if it's the beginning of May, the end of May, the beginning of June, I don't know when it is but we got a whole bunch of season left and the time that really matters is the playoffs.

That said, with proper rest, treatment and physical therapy, Teixeira should eventually return to form. He may be at increased risk for similar injury in the future, but the excellent medical he is sure to receive should minimize the likelihood of any complications.

Regrettably, the most pressing question—where the Yankees will find themselves in the standings once Teixeira is cleared to return—will not be answered for some time. Yet regardless of how far the Bronx Bombers may fall, rushing Teixeira back to the field could prove disastrous.

Just ask Jose Bautista.

Dave Siebert is a medical featured columnist for Bleacher Report who will graduate from medical school June 15. He plans to specialize in both Family Medicine and Primary Care (non-operative) Sports Medicine. Injury and anatomical information is based on his own knowledge except where otherwise cited.